This invention generally relates to rotary compressors, and more particularly, to rotary, screw-type gas compressors which inject a lubricant into the compressor both to cool the compressor and to provide a seal within the compressor.
During rotary screw compressor operation, a pair of intermeshing lobed rotors rotate within a compression chamber. As the lobed rotors rotate, lubricant is supplied to the compression chamber to maintain a seal between the rotors and to cool the compressor. The lubricant is later expelled from the compression chamber by action of the rotors. A reservoir tank or receiver storage tank receives the compressed gas and lubricant expelled from the compression chamber.
If the compressor is being used to supply air at a desired pressure, the compressor will operate until the air pressure in the reservoir reaches a desired level. This operation is referred to as a "loaded" condition. Once the air pressure in the reservoir has reached the desired pressure level, the opening of the gas inlet to the compressor is reduced or closed so that the amount of air compressed will be reduced. This operation is referred to as an "unloaded" condition. The compressor will operate in this manner until the air pressure in the reservoir falls below the desired pressure level, at which time the gas inlet is reopened and the compressor will operate in the "loaded" condition.
Rotary screw-type compressor performance and efficiency may be maximized by performing one or more of the following actions: reducing oil supply temperature as much as possible to avoid preheating intake air; optimizing oil lubricant flow at all combinations of rotor speeds, system pressure, and load conditions; or by maintaining discharge temperature above dew point but below the maximum safe operating temperature for an oil lubricant to assure that condensation does not occur in the system.
In present compressor designs, a minimum desired discharge temperature is achieved by use of a constant temperature thermal mixing valve and a fixed supply oil restriction. Maximum discharge temperature is controlled by using a sufficiently large cooler which is able to maintain a discharge temperature less than the maximum allowable in high ambient temperatures. However, these present designs are typically ineffective in increasing compressor efficiency because these compressor designs permit higher than optimum oil supply temperatures to insure that no condensation forms in the system, and the present compressor designs permit higher than desired oil flow to insure that the compressor discharge temperature is not excessive at high ambient temperatures. However, excessive oil supply temperatures and excessive oil flow to a compressor reduces overall compressor efficiency.
The foregoing illustrates limitations known to exist in present oil-flooded rotary screw compressors. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.